Abstracted from A Scientists View of Almost Everything by Mark M Green
Tension is a good word to describe what explosions are all about. Tense molecules blowing themselves apart cause explosions, and forming what could be called relaxed molecules, like nitrogen, N2, which is most of the air around us. Tense molecules are high-energy, and relaxed molecules are low-energy, and when high-energy molecules find a way to change into low-energy molecules then things get hot. A lot of that energy difference is turned into heat. Some molecules have plenty of nitrogen in their structures but the nitrogen is not in the relaxed state of two together, N2, like the nitrogen in the air. Instead the nitrogen atoms N are kept apart from each other in different cells of a molecular prison, aware of each other, in an anthropomorphic sense, but kept apart by an insurmountable force. Molecules that have nitrogen atoms, N, imprisoned in the molecular structure, are the best explosives and especially if oxygen atoms, O, are tied up in the molecular structure as well. These molecules have a good reason to explode. As the explosion begins, initiated by a spark of some sort, the extreme heat released at the first instant blows apart more of the explosive molecules, which release more heat as they explode and so on until all of the molecules join the party and explode together in a very short time, even fractions of a second, like the lighting of a match. All the explosive molecules fall apart, the molecular prisons disappear, torn apart by the heat and by the oxygen atoms grabbing all the carbon atoms, C, and forming carbon dioxide, CO2, and grabbing all the hydrogen atoms, H, and forming water, H2O. And all the N atoms that used to be constrained in their molecular prisons have a chance to move about and find each other and become N2. And they all join in that shock wave driven by the heat to move at incredible speeds—consider 8000 meters in a second destroying all in its path.
Great explosives should therefore contain plenty of nitrogen, N, and oxygen, O, in their molecular structures. This is the reason that an arrangement of nitrogen and oxygen atoms that chemists call nitro groups, -NO2, turns low-energy molecules containing carbon and hydrogen into high-energy explosives. Add three of these nitro groups to glycerol, a very low energy molecule, a byproduct of soap manufacture found in many of the bath products we use, and get trinitroglycerine. Alfred Nobel found a way to tame trinitroglycerine. His method converted an uncontrollable material apt to explode without warning, to a controllable explosive, dynamite. This made Nobel wealthy beyond imagination with his ability to fund the Nobel prizes.
But there are many more possibilities for these -NO2 groups. Add multiple nitro groups to cellulose, which is found in wood and you get gun cotton, nitrocellulose. Add three nitro groups to toluene and get TNT, trinitrotoluene, and don’t forget to add three of those nitro groups to phenol and get picric acid, trinitrophenol.
When there is a rapid chemical path allowing the atoms in a molecule to form low energy molecules, heat must be released and an explosion will follow. Mines have often been the victim of a completely different kind of explosive molecule, one that contains no nitrogen or oxygen but one that is commonly found where coal is mined. Firedamp, mostly methane, CH4, contains no nitrogen at all. For methane, the energy powering the explosion arises from the four H atoms combining with oxygen in the air around us to form H2O and the carbon atom similarly using the oxygen to form CO2. Water and carbon dioxide are exceptionally low energy molecules and therefore forming them from methane releases a great deal of energy, the energy necessary for the explosive force. The tension arising from methane surrounds us in New York City where pipes containing methane are buried under the streets all around us. The reason a smelly sulfur compound is added to the urban methane is to alert us of the methane leaking into the air and therefore access to oxygen, leading to the potential for the explosive force in the conversion of methane to carbon dioxide and water.
For now let’s focus on the nitro containing kind of molecule, where the oxygen in the air is not necessary, so that the explosion can take place in a contained space. If one or more of these explosive molecules fill a shell hurled great distances from a cannon or is dropped from a war plane from great heights, or fills the nose of a rocket, or fills a landmine or helps to open a path for a road, it makes no difference; the nitrogen and its gaseous friends just take their wild ride one more time. Get out of the way if you can.
Many in Ukraine cannot get out of the way as their lives and homes are destroyed by the force of these explosions raining down on them, attempting to make them surrender their country to a Russian autocrat.